Production of aviation gasoline



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PRODUCTION OF AVIATION GASOLINE Filed March 27, 1944 mcrnow.

4%.... o mm coIudLL InvenTor'. lIvcn* G. Nixon Bg his AH'or'neHL Patented July 23, 1946 AUNITED sTATEs PATENT OFFICE,

PRODUCTION OF AVIATION GASOLINE Ivor G. Nixon, Ewell, England, assigner to Shell Development Company, San Francisco, Calif.,` a

corporation of Delaware Application March 27, 1944, Serial No. 528,290

tested at their detonation limited power outputs,

in a Cooperative Fuel Research .Committee (C. F. R.) super-charged 3-C engine.4 The test was carried out according to the Coordinating Research Council method designated CRC-F-4- 143, and described in the report of August Vv2,

1943 of the subcommittee on Blending Octane' Numbers of the Aviation GasolineA-dvisory Conn mittee to the Petroleum Administrator for War. Index numbers areapproximately equal to the percent of power that the fuel can produce as compared with the power produced by iso-octane underthe same conditions.

Index number differs from octane number in that the lformer is a measure of the allowable output of a super-charged aviation engine under take-off and climb conditions while octane numb erv is a measure of the detonation tendency of the fuel in a nOn-Super-Charged'engine under cruising conditions. Thus octane numbersand index numbers referto very diiferent fuel properties. Y

It is well known that naphthas used inthe blending of high grade motor fuels,` and particularly aviation gasoline, must have a high antiknock value, must be free of gumeforming components, and must maintain their anti-knockv down and cleaned as'soonyas deposition `of'coke properties under severe engine conditions, i. e.V

high temperature, high compression and rich mixture. For these reasons naphthasV rich in aromatic hydrocarbons and substantiallyfree from olefins are preferred. Aromatics are known to have excellent anti-knock properties which dol not decrease under severe operating conditions and have' no tendency to form gums or to deteriorate otherwise during storage.` Olefins, on

the contrary, frequently oxidize andpolymerize fr during storage, forming gums, and thus render a motor fuel less desirable for airplane engines..

It is well. known that by suitable thermal treat- Y ments 4Which may involve carbon-carbon scission and dehydrogenation or isomerization or polywhen conducted by'iconventional methods, us

ally cause the formation of large amounts of oleiins.

gasolines,

It is also known that for a given hydrocarbon feed, a practical limit is placed on the attainable vseverity of cracking conditions because Vof coke deposition. There is a certain severity of cracking above whichcoking becomes very rapid, and.

ybelow which it `is very slow. .This critical value may to some extent depend upon'the desgnof the furnace inwhich the cracking is conducted,

but for a given furnace it isa function of the nature of the feed.` Sinceafurnace must be shut begins to plug it, it is obvious that only processes in which coking is relativelypslow are economically practical. However, more severe cracking.

conditions can be maintained without objectionf able coking by any one or more of the following methods:v (1) introducing into the cracking zone,

together withV the naphtha, flow" boiling hydroY `carbonscontaining from 1 to'about 5 vcarbonatoms per molecule; (2) reducing the amount of Y olens present in thenaphthaLto-be cracked ;'and Y (3) l.increasing-the aroma-tic content of the fractionto be cracked.y A l It has been discovered'that-if certain selected naphtha ,fractionsV having'ilow olefin content are cracked and recracked under certain conditions,

a relatively high boiling fraction may be obtainedv .that has a high concentration of aromatics, a low concentration of olens and a greatly increased index number.

It is an object of the present invention to provide an improved methodV for making aviation blending stockhaving a high rich mixture rating in supercharged engines, that is, a blending stock having ahigh index number. Itis another object to produce naphtha having superior anti- `knock andy storage properties.' Another object isto provide a cracking process capable of producing a naphtha having high aromatic content and unusually low olefin content from which ,purei aromatica' particularly toluene, may be obtained, if desired. Still another object is to produce a maximum amount of aromatics and high index 'I number components from 'a naphtha fraction with a minimum amount of re-forming capacity.

The process of this invention comprises the lfollowing essential steps:

1. Thermally cracking a'straight run naphtha having a selected boiling range;

For this reason, thermally cracked naph-i thas have not generally been used in aviationV lfllhe. natureVV of 'the .invention willV be Y 11:? Therstraight runchydrocarbonl napht s 2. Fractionating the resulting cracked products to obtain a'selected naphtha fraction; y Y

3. Rea-cracking said second fraction, preferably Vin the presence of a light feed;

Y 4. Fractionating the resulting re-crackedprmi-V `uctsto produce light aviation blending stock and a relatively heavy ,Y fraction boiling essentially within about 140 and 225 C.;

5. Further re-cracking said heavy fraction,r

Vpreferably in the presence of a lightieed; and Y 6. Fractionating the Yresulting cracked heavy'Y Vfraction to produce a heavy Yf,aviatio nYbleriding- Y stockof high index number.

.r 'In addition to these essentialv steps, there'may be inserted between'steps'4 and 5' a treating stepY wherein both Ythe lightandheavy fractions are treated vto remove small.V "quantities 'ci .olefins be fractionated andtreated to improve its avia-VVV ti-onblending characteristicsz 1 i Y, .Tl`iermalf-=V `rcracking vmeansV non-catalytic cracking. o'rcracking in the.A absence-oi"- a catalyst "asun'derstood in theV conventional sense, in ao-- cordance with the accepted usage in the prior art as exemplified. by the denition found onY page?! f Whichmaybe present before they Yare' separated. f, Further, Ithe iinalheavyraviation base stockmay offThe, Chemistry ofV Petroleum DerivatiJzes-by Carlton Ellis, publishedin 193s.

The .success oirtheV present*k invention, and! particularly ofx'the re-cracking, dependsy onV the properl selection ofrthefstraight run'v andr the.'-

crackednaphtha fractions. 'It is only` when alli 1 three' ofgthesefractions are-properly chosen crackedrunder the proper.conditionsfthat the full benets of this inventionare obtained..

ing stocks or which yield such aromatics in the subsequent cracking steps of the process. Ii the cracking stock is very rich in olens, then the product of re-cracking, that is the aviation blending stock, will also be relatively rich in olens. Also more coke formation will be encounteredY which will, in part, limit the index number that caribe obtained in the process. ,That this must be avoided has -been pointed out before.

Thus the boiling range of this starting material lies in a range essentially within about 96. and

230 C; If the boiling range is high, say essen-k tially within about 150 and 236 C., an increase in the, yield of the heavy aviation blending stock Y `is obtained/.at the expense of a decrease in the c ,yield of the light aviation blending stock which v maybe removed between steps l and 5, menf For example, if .the initial boiling tioned above. point ofthe starting material is above theV boiling point of toluene, say at about 1l9 C., then the yield of vthe heavy aviation blending stock almost twice that compared` to the yieldobtainedk from a starting material having aninitialboilingVVV Y point at 5 Cland includingtoluene, While the total yieldofrrlight and heavy aviation fraction remains about the same. r 1 y In the rstrstep of thisV process, the selected straight run naphtha fraction .is introduced throughline l tintov a cracking zone sucha'sa crackingcoili whereinrit is cracked in a pseudo liquid phase,l (that is,"l-cra`ckedl above the critical Y temperature and pressure 'of. the naphtha-fracbetter unt derstoodefroin thedfolloivingdetailed description, v

of. a `preferred embodireboilers, '"condensers, and 'otherauxiliariea Ythe proper ,placement of.; which ,willvv at= dent tdthoselskilledin theart.'

fonce .be eviforms the starting material of thepresent process maycoriginateirom, anycrudathougharomatic or naphthenic.' oils are :preferred=.to.parair1icones.' Floriinstance, a. 4straight run: 'naphtha fraction tion) under conditionsvas severe as ispractical withoutexcessive coking. Il desired, the time off vcracking may be extended andg'controlledi with theuaid or a reaction or soakingY chammr notiV shown.Y Forrinstance, these crack-ing conditions have been found` tocorrespondto lcrackim'g temperatures'between-.about 5409 C.V and580 and; v inlet pressures between# about 54) and Yi100;

Lrg/sq. crn. Y Y Y ln the secondV step, the

@ucts froml'zone Klare Wthdrawnthrough line,- 53'2- a. which' having.' a U.;O. lE...characterizatio'ni.factor Vbelof-.xz

- Y1.1;6 andi preferably. below, 171.4; is.' preferred. The

U. O. l?. characterization. factor is Aacm'easureloi` the parafnicity of an oil. A highly paraiiinicjoil hasa, factorof,=l2.5 and aA highly aromatic and;

naphthenic Yoil has a lovverfactor .approaching li) asa, minimum. leum f ractions. by Watsonghlelson:Murphy ,oi/U, O. P,.,'Ind, 'and Eng.` Chem., vol..2"!', llo-l2,

; Furthermore, this 'starting `material` orfiirst naphthafraction should p leferably have an *AQ S.

Y 'Il-' flv/Luinitial bolingpointpf, not below Soi C. and --preierably notbelow 190,? C. its end boiling. point distillatii Shouldbe below about and preferably belowy about 290 C'. The

reasonsforthese limitationsare asY follows: h rst,V

most of therihyvdrocarbons boiling youtside these limitstend upon craclfnng to4 produce' relatively i See. Characterization of. lpetrvoe'f large amounts of olens boiling within the boiling range of, the cracked naphtha selected.;for.` the 'subsequent cracking steps andsecond, that this fraction contains most. of ythe'.ar.ornatic hydrocarv bons which are valuable for.l aviation'fuel blendand are quenched` and fractionallydistilled in the distillation column Zilto separate therefrom those products boiling aboveabout 230 C. and preferlably above Zf C. whichY are Withdrawn from thev bottomof the column 2li through line 2 l. The remaining lighter portion of the products is Withdrawn from the top of the column through line? 22- K andfintroduced into another fractional distillertion column whereinthe, products boiling Vbeflow about $0", Grand-preferably belowY about-193l of. columnlrZ.V rThe remainingfraction,` which;

has a boiling range.essentially-within aboutQGTC;

and 230. C. will be referred to hereinafter as thel second naphtha fraction, and is?` withdrawn fromV the bottom of` column 25 through vline Z-ll lTheY ,'gases.V and 'light hydrocarbons Withdrawn Y from the topfof. column 2,5,throughilinel2 mayv 4'be separated rand employed in other processes.

For example, the C5 and lighter hydrocarbons may be alkylated to producea blending stock for. gaso-V line, or, any C5 orhigher hydrocarbons. maygbe employedas a blending. stock formotorfgas'olines if desired. The C4, hydrocarbons mayV becohvertedl into octylenes, cracked to produce.- butadiene, 'on Valkylated to produce aviation blending stocks.

The C3 hydrocarbons may be. chemically treated'A toproduce. acetone; and the. C1y and (lajhydro-k carbons maybe employed. as'fuel. Still further,

thehydrooarbons having `from 3.to5.carbon atoms per moleculemay beemployed again inl this proc.- essasthe light feed that is preferably introduced resulting cracked prodkj into the next two cracking steps as described below. Y,

This sec ndy naphtha fraction usually hasan octane number of at least 74 or '75, and can be used Vwith advantage as a motor fuel, but not as aviation fuel. It is characterized by a relatively highlcontent of monocyclic aromatics and naphthenes, asV opposed to naphthas boiling above about 230 C., which contain a relatively large amount of polycyclic aromatics and naphthenes. These latter compounds should not be included in the selective fraction because upon cracking under severe conditions they tend to promote coke formation and lower the quality of the final product. Moreover, as pointed out before, relatively high boiling hydrocarbons tend to form large amounts of oleiins upon cracking, which boil within gasoline boiling range. Y Y

By further treating this second vnaphtha fraction as described below, its octane number can be greatly improved, its aromatic content increased, and itsparaflin, naphthene, and particularly oleiin content decreased so that it can be used for aviation fuel. AIn the third step, the second naphtha fraction is introduced into a second cracking coil 30 through lineY 3|, wherein it isre-cracked under conditions similar to those maintained in cracking zone I0. It is desirable, although not necessary, to add to this second naphtha fraction, through valved line 32 before it enters zone 30, a minor amount of light hydrocarbon feed consisting essentially of atleast one hydrocarbon having from l to 5 and preferably from 3 to 5 carbon atoms per molecule. The amount of the light feed employed as previously indicated is merely sufficient to reduce the speed of coking for economical purposes, and otherwise has no material effect on the properties of the selected cracked naphtha fractions.

tween 5'and 15% by volume of the feed to zone The re-cracking operation in zone 30 should be conducted under the most severe conditions which can be tolerated without excessive coking. These conditions may be more severe than those in the `first cracking zone I because many components of the original fuel, which tend to decompose readily, and cause coking, have been cracked in the rst cracking step and eliminated in the fractional distillation columns 20 and 25. The con- Vditions correspond, for example, to temperatures ranging between about 540-580 C. and pressures ranging between about 40 and 100 kgs/cm?. The resulting recracked products are withdrawn v through line 33, quenched, and fractionated as described in the second. step.

The severity of the cracking may be defined either by the crackingV conditions, or by the changes brought about by these cracking conditions in the properties of the hydrocarbon and particularly in its boiling range. The latter method is particularly applicable when the feed stock has a relatively narrow boiling range, because in such a case, portions whose boiling ranges are changed are most likely to boil outside the boiling limits of the feed. When dened according'tothis method,

'the cracking conditions which, for this process, 'are such that a cracked fraction having the same boiling range as the naphtha feed amounts to about 50% to 90% of the cracked products in 'each cracking operation, and preferably about 70% in the first operation and about 60% in This amount mayv rvary between about 5 and 30% and preferably bethe second operation. In the third cracking operation, the change in boiling range is less sigeniflcant because of its `relatively high aromatic content.

Another way of determining the severity of cracking includes methods of determining the aromatic content of the cracked product. Some of the ways of measuring this aromatic content 'are as follows: v

One method is by measuring the change in octane rating of the fraction after it is cracked. In general, the octane rating is determined for a debutanized fraction having an end point of 200 C. For example, the second naphtha fraction produced in the process of this invention should. preferably have an octane number of vbetween .74 and 78 by the C. F. R. motor method. Y

Another method is by measuring the aromatic content by percent by weight of the cracked product which is extractable in 98% sulfuric acid. This method is not very accurate, because the strong acid tends to polymerize some of the olens, causing them to remain in the oil phase. However, if the bromine number of the cracked product is below about l0, the weight percent extractable is within about 5% of the amount of aromatics present in the cracked product.

A more accurate method is by means of the specific dispersion which is a measure of the percentage of aromatics inthe resulting product (see Ind. and Eng. Chem., vol. 29, No. 3, March, 1937, .p11 319-325). For example, a fraction which has a specific dispersion of about 135 contains at least about 50% aromatics. Thus, the selected third naphtha fraction obtained from the products `of zone 30 should havea specific dispersion of at least about 135 and preferably at least about 140.

It is essential that each cracking operation described in this process be carried out as a separate step. If it were attempted to maintain cracking conditions sufficiently severe to produce the desired result in one operation without intermediate separation of light and heavy components, heavy and tarry components produced in the initial stages would cause rapid coking in the subsequent stages. Moreover, the light unsaturated components formed at the beginning would be present in a large concentration, would polymerize to form olens boiling within the naphtha range, and thus would produce finally a more unsaturated naphtha, which is not desired.

In the fourth step, the cracked product from line 33 is introduced into the fractional distillation column 40 wherein the products boiling above about 230 C., and preferably above 200 C., are removed through bottom line 4| and the remaining portion is withdrawn through top line 42 into the fractionating column 45, wherein the lighter hydrocarbons boiling below about C., and preferably below C., are withdrawn through Vapor line 46 to produce the third nap-y tha fraction which is withdrawn through bottom line 41.

This third naphtha fraction has an olefin content much lower and an aromatic content much higher than that of the corresponding fraction obtained from the products of the first cracking zone l0. This third fraction should have an octane number, by theV C. F. R. motor method, at

haveaspecific'dispersion of atleast 140 and 'Vpreferably l50orabove. a AIn a preferred, although not essential embodiment of this process, the third naphtha fraction is subjeeted'to a refining treatment. Thus, as

illustrated yin. `the drawing, thev third naphtha fraction from the bottom' of column 45 is passed through lines il and5l to a treating unit'.

The type of treatment employed depends largely upon the properties of the third naphtha fraction. For instance, if `this fraction 'should contain'considerable amounts of oleiins, a treatment Vadapted to'remove ithe major part'of the olens is preferred. Such atreatment, for example, is

, a light sulfuric acid treatment. Although a sulfurie acid 'treatment is known ordinarily to reduce the octane number of cracked gasoline, it does, on. the contrary, further raise the octane number of the third naphtha fraction prepared according to this invention. 'A suitable sulfuric acid -treatment lmay involve the contact of the fraction with between about 1 and 5% by volume be separated; selective hydrogenation in the presence of a-suitable hydrogenation catalyst, suchl as Vfinely divided nickel, chromium oxide, molybdenum or tungsten sulfide or a combination of these, etc.; treatment with catalyst of the clay type'under conditions which do not cause substantial cracking; destruction or removal of harmful sulfur compound by doctor treatment, extraction with alkaline Vsolution in the presence of a solutizer for mercaptans, lor oxidation -in the presence of copper catalysts, etc.

The specific conditions involved in the treating processes as above mentioned may be readily obtained from the book, Chemical Refining of Petroleum, vKalicl'ievsky and' Stagner, published by Reinhold Publishing Corporation, 1942. In this book are descriptions of processes for the treatment of hydrocarbons with sulfuric acid (see Chapter II), with alkaline reagents (see Chapter IV), sweetening processes (see Chapter V), rening by adsorption (see Chapter VI) and relin- Ving with a solvent (see Chapter VII).

These treatments may be relatively light, i.e.

'bottoms from the rfa-distillation are usually high.Y ly aromatic and may beblended into fuel oils.

If desired, the untreated third naphtha fraction, or the treated andre-distilled naphtha fraction may be withdrawn through Valved lines yil or 5I and 52 to the toluene recovery plant 53, wherein toluene is extracted and withdrawn through Valved line 54. The remaining non-toluene portion of the third naphtha fraction is .returned 4to the process "through valved line 58.

f A portion of the third'naphtha fraction (treated or untreated, and/or containing toluene or not) may, however, be removed from Ythe system through valved line 59 and employedras an aviation blending stock, in that it nowh'as an' octane number between about and 85 and an index number, in a blend with 4 cc. of tetra ethyl lead/gallon, between about and 135.

Continuing the operation ofthe process of'this invention, the untreated, or preferably the treated thirdna'phtha fraction i'spassed into the fractionating column 60 Vthrough valved line 6l, `whereinit is separated into a light aviation base stock and `a heavy fraction. The out point for this separation may range 'essentially within about 140 and 155"y C., but preferably whereinthe xylenes 'and eumene which have high index nmbers, pass overhead into the light aviation baseV stock (for'instance, at about 150 or 152 C.) This light aviation base `stock is withdrawn through vapor line 62 and if desired may be .further treated or may be blended directly into aviation or yother motor fuels. Y

The light aviation base stock should have an octane number by the C. F. R. motorvmethod between about 80 and 85 and should havean index number in a blend with 4 cc. of tetra ethyl lead of between aboutl and 140. Between about 50` and 75% of the light aviation base stock should be extractable with strong sulfuric acid, and it should have a, specific dispersion above about and preferably above 150. The boilf ing range of this base stock may lie between about 90 and 155c C. and preferably between 100 and l5 C., although its end boilingr pointmay be as low as 140 C.

The heavy naphth'a fraction Withdrawn from the bottom of column 6U, which hasa boiling range essentially within about 140 and '230 C. and preferably essentially Within about and '200 C., usually has an octane number by the C. F. R. motor method within about 80 and`85, but its index number in a blend with 4 cc. of tetra ethyl lead is usually much lower than that of the light aviationfbase stock withdrawn from the top of column 6B. Thisheavy aviation `base-stock usually has an index number ranging only be-V tween about 1-10 and V125. The aromatic-contentof this heavy fraction from the bottom of column 60 is much higherthan that of the light aviation base stock, in that it has/a specific dispersion of-at least 15) and preferably aboveand it is between 65 and 95% extractable with strong sulfuric acid.

In the fth essential step, the heavy fraction withdrawn from the bottom of columne through lines 63 and 'H is introducedrinto a third'cracking coil l. As in cracking Zone 30, it i's'also desirable, but not necessary, t0 introduce Ywithr the'heavy fraction in line 63 a light hydrocarbn through valve line "i2 consisting essentiallyiof at least one hydrocarbon having preferably from r3 to 5 carbon atoms per molecule. The amount -of this added light hydrocarbon should range between about 5 and -30% by volume, and preferably between about 5 'and 15% by voluineof the feed'to cracking zone 170.

It is possible, 'but not preferred economically, -to employ the treated third naphtha fraction from :line el as the feed to cracking zone Tllby by-jpassingthe column `60 through line 13.

The cracking in zone lil is generally'carried vapor line 86, andan intermediate fraction withdrawn 4through bottom line 81. This Vbottom product is a vheavy aviation base stock usuallyV having an octane number above about 80 and an index number in a' blendcontaining l1 -cc. of tetra ethyl lead/gallon,between about 150 and 165. The index number range is considerably higher than the index number of the light avia- 'tionbase'sto'ck removed from the top of column (il), orthe third naphtha fractionfremoved from line 59 or the heavy fraction in line 63.

vThe lighter hydrocarbon withdrawn through lines-46 and`86 of columns 45 `and 85 may be ioinedfwith those from the top of column 25 in vlines 2 I,

si'red, 'i nto fuel oils or used for any other suitable purposes. Y i

The heavy aviation base stock maybe Withdrawn from the system through valve line 88 or it may be subjected to treatment similar `to that described for treating unit 50. If the heavy ibase stock is treated, it is passed through valve "line 89 into thetreating unit 90 and then passed vinto the re-run column' 95 similar to column 55.

Thistreatmentof the base` stock does not materiallychangeits octane number orits index V'line 26 and separated for use in the same manner Aa's those described from line 26. The heavier fractions withdrawn from 4l and r8i of columns 2U, .'40 and 80, respectively, are highly aromatic and may be blended, if deetc. Many of these blending agentsmaybe obtained or produced from the icy-products o'f'this cracked in a iirst cracking zone having atransfer temperature of about 548 C. and an inlet pressure of about 51 kg./sq. cm. to produce a cracked product which was fractionated to obtain a second naphtha fraction having the properties 4disclosed in the table below. This second naphtha fraction and a mixture of C3 to C5 cut amounting to about 14% of the feed was then cracked'in a 'second cracking furnace having a transfer temperature of about 5419 C. and an inlet `pressure of about 63 lig/sq. cm. to produce a re-cracked Y product which was fractionated to obtain a third naphtha fraction having the properties disclosed in the table below. 'This third naphtha fraction Was then acid treated with about 2% by weight of 98% sulfuric acid and re-distilled to remove lanyA high polymers formed during the acid treatment. This treated fractionwas then further fractionated into a lightl aviation Vbase stock and a heavy fraction having the properties disclosed in the table below. The resulting heavy fraction and aV mixture of C3 and C5 gases amounting to about 11% of the feed wasthen passed through a third cracking furnace vhavinga transfertemperature of about 545 Q. and an inlet pressure of about 76 kg./sq. cm. to produce a cracked product which was fractionated to obtain a heavy. aviation base stock having the properties disclosed in the table below.A

Straight I Light Heavy rltiln!1 nssfglia n'ga avliation tHezvy aviation na t a ase rac lon ase fralztion traction fraction stock stock l .Specic gravity 0. 786 0.807 0. 824 0.805 0. 844 0.858

' f C A. S. T. M.: P34. f I. B. --O- 120 77 110 97 146 130 10%- -C 134 123 121 108 154 148 O 157 146 139 117 160 157% 90% -C 210 209 166 138 170 169% F. B. P C 180 152 179 180 'Bromine number; 0 25.4 6 6% 5 4 Percent byw.extractablew h98% HzSO4 18 49 60 y 53 69 86 (Reed.) vapor pressure 8 V1. 2 0. 3 0. 4 Octane number (clear, A. S. T. M

-` Y motor method) 52.6 75.8 81.5 80.5 83.5 90 Index number (in blends containing 4 cc.

TEL.) f 129 136 119 157 niimbergfrom what it; f f fI 'h e treated vproduct may be withdrawn from fthe top of vcolumn l95. throughyalve line `9 6 ,or .it `'may be passed throught valve line 9,1 `into a blend- "ingplant I .iwhereitLisi mixed with other base llnarblend. y as before the Ltreatment.

stocks to produce a finished aviation gasoline.`

jSome suitable Vblending yagents toV `produce a 7iinished aviationggasoline include light straight run gaso1ines, `isopentane, cyclopentane, neohexane, '2, Bedimethyl butano, di-isoprop-yl ether,

triptane, iso-octane, alkylationgasoline produced by reacting isobutane with" C5 and lower olens, etc. These blendingagents give the proper boiling range tothe final blend and its octane numjbe'r may be further improved by the addition of tetra-#ethyl lead, aromatic mono-cyclic amines,

From the above tame, it may Vte' yseen that the index number of thel heavy aviation base. stock Y is materially above that of the third naphtha fraction or even thelight aviation base stock. Furthermore, it may berseen that the high boilf ing range of the heavy aviation base stock lends itself well forblending with iso-pentane andfsirnilar volatile blending stocks. i

Example II j by volume of a light hydrocarbon feed consisting l predominantly of propane andnpropylene, vbut j ,also including soniei'C'i; and Cs' hydrocarbons, was further cracked in a cracking coil ata temperai `ture* of ab.outv540 C. and an inlet pressure Vof 76 1kg/sq. cin. The resulting 'cracked product was Y; thenfractio-nated toob'tain a heavy'aviation gasi oline base stock having the ,improved properties Y l shown inthe table below.

that the index number of theheavyY aviation f i base stock is better than iso-.octane containing 4 4 cc. tetra ethyl lead. The resulting cracked'p'rodl yuct wasthen fractionated to obtain a heavy avia-V .-tion gasoline lb ase .stock having` the improved "fpropjertiesshown Yinthe 'table below.V

Y Heavy Heavy avlationf .fractlonr base stock Specic'gravity l0. 8,47 0. 858

Y 1504 68 87.0 `(Reed.) Avapor pressure Octane numbericlear, A. S. 4T.,M.-- i vC. F.R. motor method) Y -83. 5 91:3

'index number (in blends, c t ming 4 Y Y `'l"EL)K Abovel54 It shouldV be .g noted i `I claimas my invention:

230.C;, comprising thestepsof ncnfcatalytically Aing i the resulting ,further-gcracked 1product by itself to produce aviation base stockkgboiling essentially within .the vrange ofabcut 1.00 Q. i and .20.0 C.,. each.of.said cracking-practices being conducted at a temperature between about 540 gC. and i5180 C. and at a pressurebetween about 40 and 100 kg./sq. cm.

2. The process of claim 1,-wherein the `firsty cracking operation is conductedunder conditions to yieldazgacoline having an octane number above: about El7 4: and said second crackingroperation is conducted to yield agasoline having an octane Y *numberabove about 80. Y ,Y

3. The .process of claim.lfwhereingthe.naphtha fractions boil essentially within the range of f "about.100`C.and 200C..

l. 4, 'Theprocess of claim Lev/herein,saidgstraightrun A naphtha fraction has ar U. .0. Pjcharacterizltiongfactor below 11,6.4 i l. l i'V 15. l. A process for producing an aviation gasoline.: base stockrfromastraight run naphtha .havnsla boiling range Ywithin ,about .90 C. A and 230 C.,' comprising the steps ofnonecatalyticrally cracking.:V saidv naphtha, separating the resulting cracked product by itself :to'produce a second-naphtha i fraction'boiling essentially within the range *of about A90 C. and :23.0 C.; non-catalytically lrecracking saidsecond naphthafraction in the presence of vaininoramount of a lightfeed consist- 4 -ing essentially of atleast one hydrocarbon having .from 3 to 5 carbonratoms -per.molecule, separat- 1. Aprocess forproducing anaviation gasoline i basestock.l from la straight-run naphtha having a boiling range; essentiallywithin about 90 C; and

,5 fthe'fpre'sence of `a minor amount iof: a lightffeed- Vconsisting essentially o1" at: least k:oneghyfdrcc'arbon havingA from 13 ltori 5 lcarbon-zatorns Vper finolecule,

byitself to produce: an aviation'basexstockiboiling; essentially ywithinf the -range `of about 100` yconducted ,iatgartemperature'r between. about; 540

volumegoflthe fraction being-cracked.

n .'7. 'The 'processoffclaim whereinfsaidi-light Y `feed is between about 5%1-anri'l5%.byf:vclumezof the -vfractionfbeing cracked. 1

-8. ,A process for producing.anfaviationfgasoline base stock from astraight runinaphtha having a boilingrangelessentiallyfwithin about 90 C. and=230 C., comprising theqsteps of none-catalytically cracking said naphtha, sepa-rating'the resulting crackedp-roduct by itself topro'ducef'a second naphtha fraction boiling essentially 'Within the range of -about"90C;and 230C .,non

catalytically Vre-cr.acl:ir-1g said y*second '.naphtha product by itself to produce awthird naphth'affrac- -tion boiling essentially withinthefrangeof about 100 C. and 200 C., further separating said third ,naphtha fraction `vby itself into aY light aviation Y Y `35 base rstock boiling -essentially vwithintheY range .cracking saidnaphtha, separatir-ig the resulting l -cracked product by itself to produce .a second -naphtha fraction boiling essentially :within :tneV Q rrangeofiabout90 C. 'and 230 C., nonscatalyti- 1 cally 17e-cracking said .second naphtha fraction,` Y"separat-ing the resulting :re-*cracked product-,by itself to produce a heavyfraction boilinggbetween about 140 c and abouezo" 0., furtnernoncata- Y lytically cracking said heavy fraction and separatof about 90C. and l,155 C. anda heavy fraction boiling essentially within the range of about,1v40 f C. and 200 C.; furtherlnon-catalytically cracking /said heavy fractionfseparating the resulting ,-fur- 'V .i0L ther crackedproduct by itself to .produce .an

V a pressure between about 40 and 100 kg./sq. cm.

9. A process for producing an aviation gasolineV hasezstcckrfrcm astraieht run 'naphtha having a boiling range v.essentially within about 90 C. and 230 C., comprising the steps of non-catalytivcallycrackingsaidnaphtha, separating the re- ',sulting cracked product by itself to produce a second naphtha .fraction boiling essentially within the range of about'90'C. and 230 C., non-catav@lyticallyrefcracking `.said second naphtha frac- Ation('inlthe.presenceof -a minor amount of a light ffeedV consisting V.essentially of at least one hydrocarbon havingfromv to 5 carbon atoms per molecule, separating the resulting Y1re-cracked tion boilingessentially .within the rangeof-about Y 100 C. v and 200 C.,.furtherseparatingsaid third l fraction ioy-itseifA into a. iight aviation base stock: 1

"boiling essentiallyiwithin the range .of about 100 tiauywithin 'thefrange of about v150 aandzoo? .separating thegresu'ltingi further ciackedmrodguet and 200710.., each ofcsaidcracking operations-being.

fraction, separating the resulting re-cracked'.

Vproduct by itself to produce a third naphtha frac-V` C., further non-catalyticallycracking ysaid :heavy ature between about 540 .C- and 580 C... and at a pressure between about 40 and 100 kg./sq. cm.

10. A process for producing an aviation gasoline base stock from a straight run naphtha having a boiling range essentially within about 90 C, and 230 C., comp-rising the steps of non-catalytically cracking said naphtha, separating the resulting cracked product by itself to produce a second naphtha fraction boiling essentially within the range of about 90 C. and 230 C., non-catalytically re-cracking said second naphtha fraction, separating the resulting re-cracked product by itself to produce a third naphtha fraction boiling essentially within the range of about 100 C. and 200 C., treating said third naphtha fraction to remove a major portion of olens therein, further separating said third fraction by itself into a light aviation' base stock boiling essentially within the range of about 100 C. and 150 C., and a heavy fraction boiling essentially within the range of about 150 C. and 200 C., further non-catalytically cracking said heavy fraction, separating the resulting further cracked product by itself to produce a heavy aviation base stock boiling essentially within the range of about 100 C. and 200 C., each of said cracking operations being conducted at a temperature between about 540 C. and 580 C. and at a pressure between about 40 and 100 kg./sq. cm.

11. The process of claim 10, wherein the said treating step comprises contacting said third naphtha fraction with between about 1% and 5% by volume of concentrated sulfuric acid and redistilling the acid treated fraction to remove any polymers formed by the acid.

12. The process of claim 10, wherein said heavy aviation base stock has a boiling range between about 120 and 180 C.

13. The process of claim 10, wherein said heavy aviation base stock is also treated to remove a major portion of olens therein.

14. A process for producing an aviation gasoline base stock from a straight run naphtha having a boiling range essentially within about 100 C. and 200 C., comprising the steps of non-catalytically cracking said naphtha, separating the resulting cracked product by itselfk to produce a second naphtha fraction boiling essentially Within the range of about 100 C. and 200 C., re-cracking said second naphtha fraction in the presence of between about and 30% Vby volume of a light feed consisting essentially of at least one hydrocarbon having from 3 to 5 carbon atoms per molecule, separating the resulting re-cracked product by itself to produce a third naphtha fraction boiling essentially within the range of about 100 C. and 200 C., treating said third naphtha y fraction to remove a major portion of the olens therein, furtherfseparating said treated third naphtha fraction by itself into alight aviation base stock boiling essentially Within the range of about C. and 150 C., and a heavy fraction boiling essentially within the range of about- C. and 200 C., further non-catalytically cracking said heavy fraction in the presence of between about 5% and 30% by volume of a light feed consisting essentially of at least one'light hydrocarbon having from 3 to 5 carbon atoms per molecule,l

separating the resulting further cracked product by itself to produce a heavy aviation base stock boiling essentially Within the vrange of about 120 C. and C., treating said heavy aviation base stock to remove a major portion of the olenstherein and blending the resulting treated heavy aviation base stock to produce an aviation fuel, each of said cracking operations being conducted at a temperature between about 540 C. and 580 C. and at a pressure between about 40 and 100 kg./sq, cm. y

IVOR G. NIXON. 

